A particular type of antenna may be selected for use in an electronic device based upon a desired application. For example, a different type of antenna may be used for terrestrial communications versus satellite communications. The type of antenna used may also be based upon a desired operating frequency of the antenna.
One example of a type of antenna is a broadband antenna. A broadband antenna is an antenna that operates over a wide range of frequencies. The broadband antenna may be formed to provide increased gain along the horizon, for example, during terrestrial communications.
One type of broadband antenna is a biconical antenna. A biconical antenna has inherent broadband characteristics. However, a diameter of a biconical antenna becomes increasingly large at lower operational frequencies. A larger diameter or size may be restricted in a mobile wireless communications device as the size of the housing carrying the biconical antenna may be limited in size. To reduce the size of the biconical antenna, the biconical antenna may be truncated. As a result, a dipole-type structure is formed.
Increased antenna performance at lower frequencies may correspond to increased antenna length. However, at higher frequencies the increased length may result in the formation of lobes in the antenna pattern, thus resulting in relatively low gain on the horizon.
For example, referring now to the biconical antenna 170 in FIG. 1a, and the graphs in FIGS. 1b-1c, the biconical antenna has relatively satisfactory performance at the horizon both for low (FIG. 1b) and high (FIG. 1c) frequencies. However, the biconical antenna has a relatively large diameter, for example, 15.5″ tall by 15.3″ in diameter, for a desired operating frequency range.
Additionally, referring to the truncated biconical antenna 180 (i.e. dipole with biconical feed) in FIG. 2a, and the graphs in FIGS. 2a-2c, the truncated biconical antenna feed has relatively satisfactory performance at the horizon at low frequencies (FIG. 2b). The dominate dipole structure may be too long for the higher frequencies, which illustratively causes a lobe to form at the horizon (FIG. 2c). Example dimensions for the truncated biconical dipole are 15.5″ tall×4″ in diameter for the desired operating frequency range.
U.S. Pat. No. 7,221,326 to Ida et al. discloses a biconical antenna. More particularly, the biconical antenna includes a columnar dielectric member having frustum-shaped cavities extending respectively from an upper and lower surface toward the center of the columnar member. Flat surfaces of apex portions of the frustum-shaped cavities are parallel and in opposition to one another.
U.S. Pat. No. 7,339,542 to Lalezari et al. discloses an ultra-broadband antenna system that combines an asymmetrical dipole element and a biconical dipole element to form a monopole. The asymmetrical dipole element includes upper and lower asymmetrical dipole elements. The antenna system also includes a plastic expander ring coupled to the lower asymmetrical dipole element. The expander ring is also coupled to a canister sub-assembly. A choke sub-assembly is provided within the canister sub-assembly.